dumb question about equinoctial tides

[amadeus]

I noticed at the weekend that there was a full moon and hence spring tide on the equinox 21 September. Given that there are 13 lunar months in a year and the equinox is fixed at half yearly intervals is the spring equinox at neaps and the autumn one at springs or have I missed something? I usually check my mooring ground chains at Easter so that must coincide with the spring lows!

 

[Mirelle]

well, it was this year, but I fancy that the point about equinoctial springs is that the spring tides nearest the equinox are large tides.

 

[Chris_Stannard]

Spring tides are two dyas after the full and new moon. The factor that comes into play is the pull of the sun which is at it strongest when the earth's spin axis is such that the days are of equal length, the equinox. I remember someone proving this mathematically but I did not understand it then, and have forgotten it now. So like a lot of other things I just treat it as a fact of life.

Chris Stannard